Structural engineers assemble! Steel sheet to hold 200kg...

Russinating · 1 Jun 2020 at 19:58

If I had a 2200mm x 800mm sheet of steel bridging a gap length-ways, how thick, what type, and how far should it overlap the supports at either end, to safely hold 200kg in the middle, evenly distributed over a 300mm circle? Outdoor use, if that makes a difference.

OcUK is amazing and I'm sure someone can help me with this! May even be simple if steel is a lot stronger than I think it is.

Russinating · 1 Jun 2020 at 20:11

Fair, if it's anywhere near that then yeah, it's not as strong as I thought. May need to look a RSJs.

Russinating · 1 Jun 2020 at 23:13

Yeah fair, I didn't know if I'd just get pointed at a formula but deflection is a fair point.

So it's for the garden, to effectively make a custom surface for a cast iron pizza oven to sit in. The oven weighs 100kg so I was going double.

It'd be supported by brick walls at either end (rendered planters) and we'd probably want partial shelving underneath anyway so a vertical support directly underneath the oven is an option.

The road plates are certainly an interesting thought! Need to be carried through the house though...

Russinating · 2 Jun 2020 at 11:32

So the oven is this: https://morsoe.com/en/product/outdoor/outdoor-fireplaces/forno_uk
This is one of their official tables which is made of steel, so I don't think the material is an issue re: heatsink properties: https://morsoe.com/en/product/outdoor/accessories/outdoor-tables/morso-terra-outdoor-table

I'm effectively re-creating their bigger version of the table - https://morsoe.com/en/product/outdoor/accessories/outdoor-tables/morso-garden-outdoor-table - but cheaper, longer and more intergrated. My Sketchup below:

Mods, feel free to move this into Home & Garden at this point...

Russinating · 2 Jun 2020 at 12:38

gav_172 said:
As previously suggested I'd be using small section RSJ's or tube of some sort spanning between the walls asn then clad the top with 8 or 10mm We use 8mm at work for welding bench tops and they are damn heavy. We sit them on 40mm aluminium extrusion frames and a 1.8m long one can safely support 300kg with a safety factor of 2. 8mm x 1.8m x 0.8mm is heavy enough to try and lift, let alone anything thicker.

Yeah, I was looking at these: https://www.metals4u.co.uk/materials/mild-steel/mild-steel-universal-beams-rsj/7553-p. £97 for 2.5m. Two of those and then a sheet of steel ~1.5-3mm powder coated for another ~£150.

I love the look of corten steel but it's probably not the best as a food prep surface so might just use as a heat splashback and elsewhere in the garden.

Russinating · 2 Jun 2020 at 14:59

dl8860 said:
Two of those 127x76x13s are giving you 35kNm of bending resistance when you've got 1kNm, so it's certainly huge overkill in terms of capacity, but the key thing to think about is how you fix it all together.

In your sketchup you've got a vertical propping up under the oven, is your 2200mm span ignoring that?

Yeah I was thinking two for, purely as you say, fixing it all together, so the two RSJs run along the front and back of the 'table top'. If there was just one running in the middle then the sheet might get a bit wobbly over time or have more deflection front or back.

If the vertical isn't essential then I'd rather leave it out which gives us more flexibility over what we store under there, or what/how/where we build shelves and what made from.

Russinating · 2 Jun 2020 at 16:17

When you guys say 'box steel frame', is that literally just a wireframe cube made of this kind of stuff https://www.metals4u.co.uk/materials/mild-steel/mild-steel-box-section ? Same question as the OP applies to those as well; what sizes would I need? How easy would a ~1.5mm steel sheet be to bend over and under the edge (u-shape)?

And bricks either side.

Russinating · 2 Jun 2020 at 19:13

PlacidCasual said:
When I looked at your sketchup with the leg under the weight my first thought was cast concrete for everything, with care you can get a loverly smooth surface, you could even resin seal it. It would have a nice heft to it and none of the expansion or flexibility concerns of box section and steel sheet.

It was on my radar but would 2400x800x50mm of concrete not weigh a silly amount? It wouldn't be able to be cast in place (I don't think) so would need lifting on.

And yeah it'd need sealing since we want the part to the side to effectively be for food prep/serving.

Russinating · 3 Jun 2020 at 08:53

famas said:
Any reason you have chosen that particular oven? For that sort of money you could build a very nice Pompeii oven which would be a lot more versatile than the Morso.

The Morso being cast iron with no insulation means it will be fine for pizza and the odd grilling but it will not be able to hold any heat for retained cooking.

The beauty of a Pompeii oven is you can fire it to pizza temperatures on the first day and it will still be hot enough to roast or bake bread on the 2nd and 3rd day without the need to re-fire.

If you're going to all the trouble and expense of this outside area it's worth investigating if you're into out door cooking.

We've had the Morso Forno for 3 years and none of that is correct, other than not needing to re-fire it.

Russinating · 3 Jun 2020 at 09:56

Bug One said:
Do yo own a welder? If not, you'll have to factor that into the cost of building a box section frame.

And no, which is the trouble with that idea! Impossible to get tradesmen as it is, let alone for small jobs.